Early diagnosis of recurrent caries is essential since the rapid progress of the caries under the restorations soon results in extensive and destructive therapies. While the digital image subtraction method has already been proven to be a sensitive diagnostic tool in periodontal bone loss evaluation and in detecting interproximal carious lesions, the method has not been evaluated in diagnosis of recurrent caries where also the restorative material's radiographic qualities have an influence. The two specific aims of this project are to assess the use of digital image subtraction as a diagnostic method in detecting recurrent caries and to assess the effects of different adjacent restorative materials on the performance of this subtraction system. The ultimate goal of this research endeavour is to determine if the digital subtraction method would be valuable to the routine dental diagnostic practice. Recurrent dental caries will be simulated in extracted human teeth with chemically produced lesions at the interproximal gingival margins of the restorations, and the teeth will be radiographed with three restorative materials each possessing a different degree of radiopacity. The radiographic images of the teeth without caries will be subtracted digitally from the images of the same teeth with the simulated caries. The conventional radiographic films and the digital subtraction images will be evaluated by a panel of observers and the data will be analyzed with ROC statistics resulting in an objective evaluation of the diagnostic performance of the conventional film system and the new digital subtraction system in recurrent caries detection.